<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>三层div嵌套</title>
<link rel="stylesheet" href="box.css">
</head>
<body>
	<div class="box1">第一个
		<div class="box2">第二个
			<div class="box3">
				第三个
			</div>
		</div>
	</div>
</body>
</html>